The invention relates to amplifiers for use on a coaxial cable transmission system, for amplifying both the feed signals and the return signals carried on such system, and to such an amplifier having plug in equalizer and attenuator components for presetting the performance characteristics of the amplifier to a particular location on the cable system and for a predetermined frequency band.
It is well known practice to transmit signals in two directions, along a common electrical wire transmitting system, a typical example being a telephone system. Telephone wire transmission systems are well known for transmitting voice transmissions and also for transmitting electronically generated signals from a wide variety of equipment such as security systems, facsimile machines, and a wide variety of computer information for example, coded signals concerning credit transactions, and transferring information to and from computers connected to the telephone wire system. Due to the nature of the telephone wire transmission systems, there are significant restrictions on the speed, and volume, of information which can be transmitted within a given time span. In the past this has not been a significant problem. However, with the ever increasing popularity of the so called xe2x80x9cInternetxe2x80x9d, the ability to transmit very large volumes of information at high speed in both directions has become critical. The telephone wire transmission system does not readily accommodate itself to the very substantial expansion of the volume of information as well as the increase in speed of transmission that is required to satisfy the growing number of customers requiring Internet services. As a result, Internet servicing companies are seeking alternative means of transmission. Other communication may require the sending of reverse signals along the cable, such signals including eg. metering box and telephone signals.
Telephone wire transmission systems are also subject to intermittent interference from a variety of sources, and are sometimes simply so overloaded that they are incapable of accepting further transmissions.
Coaxial cable transmission networks for distributing cable television services are becoming widely accepted in many cities and towns, and provide excellent services for distributing television signals to television sets of subscribers on the network. Such cable television distribution systems are based on a coaxial wire cable, having a single central conductive core, and a woven sheath of wire or other form of conductive sheath, insulated from the core. Such coaxial cable is capable of transmitting much greater volumes of information at high speed, and with very little interference. In the past such cable systems have been used for one way transmission of television signals from the head end signal source to the consumers television sets. Feed amplifiers are provided at intervals to maintain signal strength, which would otherwise become attenuated, due to the length of the cable system. Such feed amplifiers incorporate equalizers and attenuators for equalizing the signals across the frequency band of the signals.
The existence of wide spread cable television signal networks has lead to the development of their use as a means of connecting consumers to the Internet system. The coaxial cable systems, with feed signal amplifiers located along the cables at spaced intervals, and with their substantial freedom from interference, lend themselves particularly well to the rapid transmission of high volume signals such as are generated by the Internet system. Consequently consumers are increasingly looking to the coaxial cable television networks as a means of connecting their computers to the Internet, so as to avoid the difficulties of connections via the telephone wire systems.
One of the problems encountered in using coaxial cable networks for distribution of Internet signals is that Internet signals travel in two directions, both to and from the consumer. This is unlike television signals, which travel in the feed direction, from the supplier to the consumer. To carry Internet signals, the coaxial cables are required to carry signals in both directions simultaneously. The consumer will be receiving signals from an Internet service provider (ISP), and will be generating return signals, generated from his or her computer, back onto to the Internet. In theory the coaxial cable networks are ideally suited to this type of two-way transmission. In practice however, there are problems which arise from the original design of such cable systems. Since the coaxial cable networks are relatively long, the feed signals on the networks gradually become attenuated and decrease in strength as they pass along the length of the cable. In the case of television feed signals this problem is overcome, as mentioned above, by the use of feed signal amplifiers located in the coaxial cables at spaced intervals. These feed signal amplifiers ensure that all subscribers on any particular cable network will receive signals of adequate strength, so that in spite of the considerable length of any one particular cable, the feed signals will all be substantially of the same signal strength to all households on that cable network.
Such feed signal amplifiers are capable only of amplifying the feed signals fed into the coaxial cable from the head end and equalizing them across the frequency band but cannot amplify return signals, passing in the opposite direction.
When it is attempted to adapt the coaxial cable system for two-way transmission of Internet signals, the return Internet signals are unable to pass through the feed amplifiers already incorporated in the coaxial network. Return signal amplifiers have been used to amplify the return Internet signals. These return signal amplifiers are located alongside the feed amplifiers on the coaxial cable network and pass the return Internet signals around the feed amplifiers, and increase the return Internet signal strength. In this way, the return signals bypass the feed amplifiers, and at the same time their signal strength is maintained at the desired level so that it can be fed back to the Internet server. Other communication may require the sending of reverse signals along the cable, such signals including eg. metering box and telephone signals.
The problem of signal strength is aggravated by the attenuation of signal strength. Attenuation varies, and is greater in the higher range of frequencies, and is lower in the lower range of frequencies. The feed amplifiers in use on cable systems are already designed to overcome these problems, and equalise the signal strength over the entire frequency band of the feed television signals. However, the adaptation of an existing cable network to accept two-way transmission of signals such as Internet signals, requires both that the return amplifiers with suitable equalizers be installed on the already existing cable network, and further that the existing feed amplifiers shall be modified so as to equalize all signals, both television and Internet, travelling in the feed directions.
Feed amplifiers for maintaining signal strength of the feed signals should be modified so as to amplify both the Internet and television signals over the entire frequency range of the signals and to equalize these signals back up to a uniform level of signal strength, across the entire range of frequency of both Internet and television signals. However, the signal strength of the signals at any given location on an existing cable network can only be determined by actually measuring the signals at that location. This signal strength will vary from one location to another. At present, the feed amplifiers are produced as a standard item, however, several such feed amplifiers are re . . . which have performance characteristics which vary from one cable location to another.
Typically, the Internet feed signals are placed within this frequency range of from about 50 to 860 megahertz, ie the usual bandwith of television signals. Certain other feed signals may also be included in the range. If the amplification of the signals does not produce a uniform signal strength over this entire range then the signals will be distorted.
The design and construction of feed signal amplifiers for cable systems is dependent upon the fact that the feed amplifiers are positioned at spaced locations along any given length of coaxial cable in the system and are located at an elevation upon a cable post, in most cases. Amplifiers with standard characteristics will not be equally suitable at each location. In fact, it will be found that before an amplifier is installed by the installer, the signal strength at that location in the cable must be tested and an amplifier must be installed having the correct amplifying and equalizing characteristics for that particular location in the coaxial cable network. These specifications will vary from one amplifier location to another along any given length of the coaxial cable.
In theory it is perfectly possible to manufacture a whole range of amplifiers having a range of different equalization characteristics. A coaxial line crew could carry a large supply of such amplifiers with them, and after testing and checking the signal strength at a particular location, could then select and insert the appropriate amplifier having the correct specifications for that location. In practice however this is not possible, since it will require a very large investment for supplying an adequate inventory of amplifiers covering a full range of characteristics, to each particular line crew. In addition, transporting such a large inventory of amplifiers covering a wide range of different characteristics, presents a problem of transporting a large number of bulky and relatively heavy objects.
A further problem is the fact that the line crew person will be required to climb up the post to reach the coaxial cable. Then the line person must check the signal strength and then come down and select the appropriate amplifier and then climb back up again and insert it. This is a slow and tiresome job.
For all of these reasons, providing an adequate number of amplifiers having ranges of different characteristics to meet all conditions and requirements on a given coaxial cable network becomes a logistical nightmare, and a severe financial strain, and causes much undesirable additional labour.
The cable networks carrying television signals are already in existence and the feed amplifiers are already in place on posts on those cables. However, as conditions change and as frequency band changes in amplification may be required.
Adapting the entire cable network by replacing all of the feed amplifiers with new feed amplifiers having modified characteristics both as to amplification and the equalization, is simply not practical.
For all of these reasons, therefore, it is desirable to provide a standardized equalizer circuit and having a plurality of plug-in components, which can simply be carried in the personal equipment of the lines person. These standardized equalizer circuits can then simply be inserted in the existing feed amplifiers by removing the existing equalizer circuits in the existing feed amplifiers, and installing the new standardized equalizer circuits. By the use of the plurality of plug-in components, each equalizer circuit after it is installed, can then be adjusted to the appropriate equalizer characteristics required for that particular location along the cable network.
Thus, after climbing up to the cable, the lines person can simply install a standardized equalizer in the feed amplifier, in place of the existing equalizer and then test the signal strength and characteristics and then insert the appropriate plug-in components to produce an equalizer having the necessary characteristics for that particular location in the system.
A lines person will be required to carry only one set of plug in components, in an adequate range of performance characteristics, so that when the signal strength has been measured at that location, the equalizer can readily be set to the correct performance, by simply selecting the plug in components having the correct values.
This greatly reduces the requirement for carrying a large inventory of amplifiers and greatly reduces the financial burden of carrying such an inventory and also reduces the logistical problems and the time consuming effort by the lines crew of checking signal strength.
With a view to achieving improvements in amplifiers for two-way coaxial cable lines, of the type having a transmission centre, and a plurality of coaxial cable lines extending therefrom, and a plurality of tap ports connecting signals from the coaxial cable line to respective terminals, and said coaxial cable system having a signal distribution system having facilities for distributing feeder signals onto said cable system and reception facilities for receiving return signals from said cable system, and wherein feeder signals and return signals passing along said cable system in opposite directions are progressively attenuated in signal strength, said system having feeder amplifiers at spaced intervals there along, for receiving feed signals passing along said coaxial cables, and amplifying the same, the invention provides a standardized signal equalizer circuit for installation in the feed amplifiers having a standard equalization circuits, which are settable to provide varying equalization specifications, and having receptacles for receiving plug in circuit components for varying said equalization specifications, and a plurality of plug in circuit components, each being adapted to interfit with said standardized equalizer circuit, and said components having a range of varying performance characteristics whereby a respective said component can be selected and plugged in to a said equalizer circuit to produce the performance specifications desired at a predetermined location.
The invention further contemplates the provision of return signal amplifiers having signal equalizers and wherein the feed signal equalizer and the return amplifier shall incorporate a circuit adapted to receive one of a group of plug in attenuator components, wherein the plug in attenuator components for the feed equaliser circuit, and for the return amplifier and equalizer shall be interchangeable between the two circuits.
In this way, a lines person can, at one time, both install a return amplifier, and a feed amplifier equalizer, and can set both feed and return equalizers to the characteristics required for that location.